General Manager Jeff Luhnow says the decision wasn't based on Houston's record but because "we need a new direction in our clubhouse."
The Astros are in fourth place in the
Bench coach Dave Trembley also was fired.
Tom Lawless will take over as interim manager. Lawless worked in Houston's minor league system and was the interim manager at triple-A Oklahoma City this season when Manager Tony DeFrancesco was on medical leave.
Adam Everett, who was working for the Astros in the minors, will replace Trembley.
Porter joined the Astros for the 2013 season after working as a third base coach for the Washington Nationals.
Boston Red Sox second baseman Dustin Pedroia was out of the lineup for the second consecutive game because of concussion-like symptoms.